The present invention relates to compositions that are useful for forming a breathable fluid impermeable barrier layer. The breathable film layer finds utility in durable goods such as tents, footwear, rainwear, etc., as well as for absorbent disposable articles such as disposable diapers, feminine napkins, and medical devices and dressings. The compositions are preferably applied as a continuous film with a non-contact coating method.
The present invention is directed to compositions that are useful for forming breathable film layers and articles constructed therefrom. The composition comprises at least one thermoplastic polymer compounded with at least one diluent or a radiation curable composition. The composition is impermeable to fluids and exhibits a water vapor transmission rate of at least 100 g/m2/day.
In one embodiment, the present invention relates to a composition comprising from about 10 wt-% to about 75 wt-% of at least one breathable thermoplastic polymer and from about 25 wt-% to about 90 wt-% of at least one diluent. In a preferred embodiment, the breathable thermoplastic polymer is water sensitive. In another preferred embodiment, the breathable thermoplastic polymer is a methacrylic acid copolymer. In a most preferred embodiment, the breathable thermoplastic polymer is a polyether block amide. The diluent is a plasticizer, wax, tackifying resin or mixture thereof and preferably a plasticizer having ether or alcohol oxygen linkages such as polyethylene glycol.
By xe2x80x9cbreathablexe2x80x9d it is meant that the composition allows for the passage of moisture vapor. The preferred water vapor transmission rate (WVTR) depends on the end-use application. However, in the context of the present invention, xe2x80x9cbreathablexe2x80x9d refers to a WVTR of at least 100 g/m2/day as measured in accordance with ASTM E96 for a 40 xcexcm to 50 xcexcm coating.
By xe2x80x9cimpermeablexe2x80x9d it is meant that the composition does not allow for the passage of fluids at a pressure of 10 psi. This terminology is clarified as needed throughout the description. For example, the Eastman AQ copolyesters are body fluid (saline solution) impermeable, yet water soluble (permeable).
The present invention employs a thermoplastic composition comprising at least one thermoplastic polymer and at least one diluent or a radiation responsive composition.
The thermoplastic compositions are particularly useful for forming a continuous fluid impermeable barrier layer. However, in many embodiments the compositions are also suitable for use as hot melt adhesives. Preferably, the barrier layer is formed in accordance with the method described in U.S. Pat. No. 5,827,252 issued Oct. 27, 1998, incorporated herein by reference.
In accordance with U.S. Pat. No. 5,827,252, the thermoplastic composition is relatively low in viscosity in comparison to typical film grade materials. Accordingly, the thermoplastic composition exhibits certain Theological characteristics, preferably falling within a rheological window. The complex viscosity at high shear rates, for example at about 1,000 radians/second, is less than about 500 poise. The complex viscosity at low shear rates, for example at less than about 1 radian/second, ranges from about 100 poise to about 1,000 poise. Thermoplastic compositions having a wide window of application are those which exhibit the appropriate rheological properties at a variety of application conditions, particularly at low temperatures. The desired Theological properties are preferably obtained at temperatures less than about 180xc2x0 C., more preferably at temperatures less than about 160xc2x0 C., even more preferably at temperatures less than 140xc2x0 C., and most preferably at temperatures less than about 120xc2x0 C.
The barrier layer may be of a conventional film thickness, for example from about 0.8 to about 2 mils. Alternatively, the barrier layer may advantageously be very thin, employing a coating weight thickness from about 1 g/m2 to about 10 g/m2. For embodiments wherein the barrier layer is very thin or for embodiments that employ a composition which is not radiation curable, the barrier layer is typically of low film strength, obtaining its tear resistance from the substrate it is coated to. However, for embodiments employing a radiation curable system or higher coating thicknesses, the barrier layer alone may exhibit sufficient film strength to be self-supporting, particularly for disposable absorbent article applications.
The resulting barrier layer is impermeable to (body) fluid and is characteristically breathable. Breathability is expressed as a function of water vapor transmission rate (WVTR) measured in accordance with ASTM E-96 for a 40-50 xcexcm barrier layer coating on porous nonwoven or of a neat barrier film layer in the case of self-supporting film layers. The barrier layer has a water vapor transmission rate of at least about 100 g/m2/day, preferably at least 200 g/m2/day, more preferably at least 400 g/m2/day, even more preferably at least 800 g/m2/day and most preferably from about 1000 to 2000 g/m2/day or higher.
In the case of compositions that are not intended to be radiation cured, the breathable composition of the present invention comprises at least one thermoplastic polymer and at least one diluent. The thermoplastic polymer, the diluent, or both are sufficiently breathable such that the formulated composition exhibits the desired WVTR rate.
The term xe2x80x9cpolymerxe2x80x9d refers to a component having a Mw greater than about 3000 and preferably greater than about 10,000. In embodiments wherein the thermoplastic polymer employed has a high moisture vapor transmission rate, the diluent is sufficiently compatible with the thermoplastic polymer but need not be breathable. However, for embodiments wherein the thermoplastic polymer is not sufficiently breathable, the diluent preferably contributes to the breathability of the mixture. The thermoplastic polymer is typically polar in nature and may also be described as breathable, water sensitive including water swellable, water soluble or water dispersible, or biodegradable.
Consistent with the definition of breathable thermoplastic compositions, breathable thermoplastic polymers are those having a WVTR water vapor transmission rate of at least about 100 g/m2/day, preferably at least 200 g/m2/day, more preferably at least 400 g/m2/day, even more preferably at least 800 g/m2/day and most preferably from about 1000 to 2000 g/m2/day or higher. Breathable polymers typically contain low reactivity oxygen linkages. The oxygen linkages are preferably along the polymer backbone, as in the case of polyesters and polyethers. However, terminal low reactivity oxygen linkages may also contribute breathability as in the case of long chain (high molecular weight) polyols, as well as hydroxylated and epoxidized thermoplastic compounds. Additionally, the applicants surmise that certain thermoplastic polymers containing silicone-oxygen linkages such as siloxane may also be suitable. Particularly in the case of employing polymers having terminal oxygen linkages, care should be taken in selecting the additional ingredients in the thermoplastic mixture to insure such ingredients will not react.
Representative examples of breathable polymers include linear saturated polyesters such as Dynapol or Dynacoll polymers from Creanova Inc, (Piscataway, N.J.), polyether block amide and polyester ether block copolymers available from Elf Atochem (Birdsboro, Pa.) as PEBAX or Hoechst Celanese (Dallas, Tex.) as RITE-FLEX respectively. Within each class of polymers, the most preferred polymers are generally those exhibiting the highest degree of gas permeability such as PEBAX 2533 SN01 and PEBAX 3533 SN 01.
The breathable thermoplastic composition of the present invention may comprise one or more water sensitive thermoplastic polymers. However, since these materials are characteristically swellable, dispersible, or soluble in water, these materials typically lack the water impermeability properties required for use as a fluid impermeable barrier layer. Hence, in one embodiment, the present invention is directed to reducing the water sensitivity of such materials to improve the water impermeability. Water sensitive polymers useful herein include a variety of crystalline and amorphous water soluble and/or water dispersible polymers and preferably a blend of a crystalline water soluble polyamide and an amorphous water sensitive polymer.
Water soluble polyamides are the reaction product of at least one polyoxyalkylene diamine with at least one dicarboxylic acid or esters thereof.
The polyoxyalkylene glycol diamine has the formula:
NH2xe2x80x94(CH2)xxe2x80x94(OCH2xe2x80x94CH2)yxe2x80x94Oxe2x80x94(CH2)xxe2x80x94NH2
wherein X ranges from 2 to 3 and Y ranges from 1 to 2.
Representative examples include triethylene glycol diamine, wherein X=2 and Y=1, and tetraethylene glycol diamine, wherein X=2 and Y=2. Commercial diamines include Jeffamine(copyright) XTJ-504 amine and Jeffamine(copyright) EDR-192 amine available from Huntsman Chemical Co., Houston, Tex. A preferred diamine is 4,7,10-trioxatridecane-1,13-diamine (TTD diamine) available from BASF, Parsippany, N.J., wherein X=3 and Y=2. Other amines such as Jeffamine(copyright) D-230, D-400, XTJ-500, XTJ-501 and XTJ-502 are also useful provided a chain terminator acid or amine is employed during the reaction, and/or additional ingredients such as waxes, tackifiers, crystalline polymers, and monoacids are subsequently combined with the reacted polyamide. For example, when adipic acid is reacted with TTD diamine and Jeffamine(copyright) D-230, the resulting polyamide is relatively slow setting with respect to reacting adipic acid with TTD diamine alone.
The polyoxyalkylene diamine is reacted with an equal stoichiometric ratio of a dicarboxylic acid. Suitable dicarboxylic acids are those having from 5 to 36 carbon atoms including adipic acid, pimelic acid, azelaic acid, sebacic acid, suberic acid, dodecanedioic acid, terephthalic acid, isophthalic acid, t-butyl isophthalic acid, dimer acid and mixtures thereof. The esters and anhydrides of these acids may also be used. Adipic acid is preferred.
The resulting water soluble polyether amide preferably has a melt point about 190xc2x0 C. or less as in the case when adipic acid is reacted with Jeffamine(copyright) XTJ-504. More preferably, the melt point is about 155xc2x0 C. or less as in the case when adipic acid is reacted with Jeffamine(copyright) EDR-192. The most preferred water soluble polyether amide has a melt point of about 150xc2x0 C. or less as in the case when adipic acid is reacted with TTD diamine. This particular combination results in a faster setting, strong, easily processed water soluble polyether amide. The low melt temperature makes this combination particularly attractive for low application temperature applied hot melt adhesives or barrier layers having an application temperature less than 177xc2x0 C.
Certain polyamides are preferred due to their contribution to the nonblocking and humidity resistant properties. Polyamides exhibiting such properties are those which are produced by reacting polyoxyalkylene diamine with at least one dicarboxylic acid or an ester thereof, the polyoxyalkylene diamine having the formula:
NH2xe2x80x94(CH2)3xe2x80x94(OCH2xe2x80x94CH2)2xe2x80x94Oxe2x80x94(CH2)3xe2x80x94NH2.
In this embodiment, adipic acid is the preferred dicarboxylic acid. However, other diacids may also be employed provided the mole percent of the additional diacids is about 10 mole percent or less with respect to the total acid content. When an additional diacid is employed at a concentration greater than about 10 mole percent, particularly at about 25 mole percent or greater with respect to the total diacid content, the resulting polyamide exhibits a longer set time prior to becoming completely non-blocking. Accordingly, it is often desirable to add an additional ingredient to increase the rate of set as described in further embodiments as follows.
Additionally, other water soluble polyamides contribute comparable humidity and blocking resistance provided a chain terminator is employed during the reaction and/or the polyamide is further combined with at least one additional ingredient including waxes, solid tackifiers, monocarboxylic acids, and crystalline polymers. In these embodiments, the polyamide is produced by reacting at least one polyoxyalkylene diamine with dicarboxylic acid or an ester thereof, said polyoxyalkylene diamine having the formula:
NH2xe2x80x94(CH2)xxe2x80x94(OCH2xe2x80x94CH2)yxe2x80x94Oxe2x80x94(CH2)xxe2x80x94NH2
wherein X ranges from 2 to 3 and Y ranges from 1 to 2.
Chain terminators include monoacids and/or monoamines and are useful in an amount less than about 5 wt-%, preferably from about 0.5 wt-% to about 2.5 wt-% based on total acid weight to control the molecular weight. Representative examples of useful monocarboxylic acids include stearic acid, benzoic acid and montannic acid such as Wax S available from Hoechst Celanese. In the absence of a chain terminator, the resulting polyamide, particularly those taught by Speranza in U.S. Pat. Nos. 5,053,484, 5,086,162, 5,324,812, and 5,118,785 are deficient in at least one property including exhibiting a high melt point, slow rate of set, high viscosity, poor humidity resistance and/or poor blocking resistance.
In addition or in the alternative, the polyamide component may be combined with at least one ingredient selected from the group consisting of waxes, tackifiers, crystalline polymers, monocarboxylic acids and mixtures thereof The monocarboxylic acids and monoamines have been found to be useful not only as a reactant as previously described but also as an ingredient to be added after the polyamide is formed.
NP-2126 as well as other grades of water soluble or water dispersible polyamides are commercially available from H. B. Fuller Company (St. Paul, Minn.).
Other crystalline water sensitive polymers surmised to be suitable for use as the thermoplastic polymer in the invention include polyethylene oxide available from Union Carbide (Danbury, Conn.) and crystalline polyesters. Water sensitive polymers that can be synthesized to possess similar physical properties such as viscosity and extent of crystallinity to that of the exemplary polyamides are believed to be particularly useful.
Amorphous water sensitive thermoplastic polymers contemplated for use in the present invention include such polymers as polyvinyl alcohol (PVOH) available from Nippon Grohsei (Japan) such as Grohseran L-301 and Grohseran L-302 and Unitika available from Unitaka Ltd. (Japan); polyvinyl pyrrolidone (PVP) available from BASF (Mount Olive, N.J.) and ISP (Wayne, N.J.); polyvinyl pyrrolidone/vinyl acetate copolymer (PVP/VA) and polyvinyl pyrrolidone/acrylic acid such as Acrylidone, both available from ISP; polyethyloxazoline available from The Dow Chemical Company (Freeport, Tex.) under the tradename PEOX and from PCI Incorporated (Tucson, Ariz.) under the tradename Aquazol, polyvinyl methyl ether available from Amoco Chemical Co. under the tradename Amobond, linear polyesters, polyacrylamide and preferably water dispersible polyesters and copolyesters (Eastman AQ) and amorphous water soluble and water dispersible polyamides.
One particularly preferred class of amorphous water sensitive thermoplastic polymers is water dispersible polyesters and copolyesters available from Eastman Chemical Company (Kingsport, Tenn.) under the tradename Eastman AQ. These water dispersible polymers are linear polyesters or branched copolyesters containing sulfonomer. Such polymers are saline and body fluid insoluble, yet dispersible in tap water. The Tg of the branched water dispersible copolyesters ranges from about xe2x88x925xc2x0 C. to 7xc2x0 C., whereas the linear polyesters have a Tg from about 30xc2x0 C. to about 60xc2x0 C. Commercial examples of solid thermoplastic linear water dispersible polyesters include AQ 35S (7,000 Mn), AQ 38S (10,000 Mn), and AQ 55S (8,000 Mn).
Preferred water dispersible copolyesters are those which are branched and exhibit an intrinsic viscosity of about 0.6 IV (Eastman AQ-14000) or less, more preferably about 0.4 IV (Eastman AQ-1950) or less, even more preferably about 0.3 IV (Eastman AQ-1350) or less, and most preferably, particularly in combination with other higher molecular weight polymers, 0.2 IV (Eastman AQ-1045) or less. In terms of molten viscosity, these ranges correlate to a Brookfield viscosity ranging from about 5,000 to about 40,000 cPs. Information relating to the chemical synthesis of the branched polyesters may be found in U.S. Pat. Nos. 5,543,488 and 5,552,495, incorporated herein by reference. Lighter color and low odor modifications of such water dispersible copolyester are also contemplated, particularly for disposable absorbent articles in which odor and color tend to be important characteristics.
The thermoplastic composition of the present invention may employ a xe2x80x9cconventionalxe2x80x9d thermoplastic polymer that is not breathable, water sensitive, nor biodegradable, provided the polymer is sufficiently diluted with plasticizers, waxes, and tackifying resins which contribute breathability. Such conventional thermoplastic polymers may be amorphous or crystalline and are typically polar to insure compatibility with the desired diluents.
Representative examples include ethylene-vinyl acetate copolymers containing about 12% to about 50% vinyl acetate such as Elvax 40 (40% vinyl acetate (VA), 55 melt index (MI), and Elvax 150 (33% VA, 44% MI), ethylene acrylic acid, ethylene methyl acrylate and ethylene n-butyl acrylate copolymers and polyamide polymers such as those available from H. B. Fuller Company (St. Paul, Minn.) and from Union Camp (Savannah, Ga.) as Unirez, and polyester polymers having low WVTR""s available from Hxc3xcls as Vestamelt or EMS-Chemie (Sumter, S.C.) as Griltex. Other polymers that are typically too low in molecular weight to employ as the base polymer include polyesterurethane polymers such as Pearlstick, available from Aries Technologies (Dury, N.H.) and polyetherurethane polymers such as Estane, available from B. F. Goodrich Specialty Chemicals (Cleveland, Ohio).
Biodegradable polymers include thermoplastic materials that are photodegradable, microbiologically and hydrolytically degradable. Representative examples include polylactic acid, polylactide, poly (hydroxybutyrate), poly (hydroxybutyrate/hydroxyvalerate), polycaprolactone, and others.
In addition to the thermoplastic polymer, the breathable thermoplastic composition of the present invention comprises at least one diluent at an amount ranging from about 10 wt-% to about 90 wt-%. The amount of diluent employed depends on the desired properties. Typically, however, higher concentrations of diluents may be employed with high molecular weight polymers, for example those having a melt index (MI) of less than 30 g/10 min, and preferably less than about 10 g/10 min. Alternatively lower concentrations of diluents are employed in combination with higher melt index (low molecular weight) thermoplastic polymers.
The thermoplastic composition of the present invention preferably comprises a plasticizer as a diluent in an amount up to about 90 wt-% and preferably in an amount ranging from about 10 wt-% to about 50 wt-%. At high plasticizer concentrations, for example greater than about 50 wt-%, the plasticizer is preferably breathable. Breathable plasticizers also typically contain low reactivity oxygen linkages.
Compatible plasticizers are typically polar in nature including a variety of liquid plasticizers including phthalate plasticizers such as dioctyl phthalate and butyl benzyl phthalate, alkyl benzyl phthalate, and benzyl phthalate (e.g., Santicizer 160, 261, 278 respectively from Monsanto, St. Louis, Mo.); liquid polymers such as liquid polyesters (e.g., Dynacol 720 from Hxc3xcls), liquid polymeric plasticizer available from C P. Hall, Chicago, Ill. and liquid epoxidized Kraton; benzoate plasticizers such as 1,4-cyclohexane dimethanol dibenzoate (e.g., Benzoflex 352 from Velsicol, Rosemont, Ill.), diethylene glycol/dipropylene glycol dibenzoate (e.g., Benzoflex 50 from Velsicol), dipropylene glycol dibenzoate (e.g., Benzoflex 9-88 from Velsicol), polypropylene glycol dibenzoate (e.g., Benzoflex 400 from Velsicol), and diethylene glycol dibenzoate where the mole fraction of hydroxyl groups which have been esterified ranges from 0.5 to 0.95 (e.g., Benzoflex 2-45 High Hydroxyl also from Velsicol); phosphite plasticizers such as t-butyl diphenyl phosphate (e.g., Santicizer 154 from Monsanto); polyethylene glycol having a molecular weight below about 2000 (e.g., Carbowax 1000 from Union Carbide) and derivatives of polyethylene glycol including Pycal 94, the phenyl ether of PEG available from ICI (Wilmington, Del.); ethoxylated bis phenol A (e.g., Macol 206 EM from PPG Industries, Pittsburgh, Pa.); dionyl phenol ethyoxylates (e.g., Surfonic DNP from Huntsman Chemical Corp.); liquid rosin derivatives having Ring and Ball softening points below about 60xc2x0 C. such as methyl ester of hydrogenated rosin (e.g., Hercolyn D from Hercules, Wilmington, Del.); toluene sulfonamide (Uniplex 214 from Unitex Chemical Corp, Greensboro, N.C.); as well as vegetable and animal oils such as glycerol esters of fatty acids and polymerizable products thereof.
Further, a variety of monoalcohols, diols and polyols may be employed as a plasticizing diluent in the breathable compositions of the present invention. Useful polyols include polyethers, polyesteramides, polythioethers, polycarbonates, polyacetals, polyolefins, and polysiloxanes. Preferred polyols are low in molecular weight and include various grades of castor oil, ricinoleate polyols (highly refined castor oil) and derivatives thereof; ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol as well as higher functional polyols having more than two hydroxyl groups per molecule such as glycerol, trimethylolpropane, 1,2,4-butanetriol, 1,2,6-hexanetriol, and mixtures thereof.
Castor oil, also known as ricinus oil, is a triglyceride (ester) of fatty acids derived from the seed of the castor plant. Approximately 90% of the fatty acid content is ricinoleic acid, an 18 carbon acid having a double bond in the 9-10 position and a hydroxyl group on the 12th carbon. The remainder of castor oil is made up of dihydroxystearic acid (0.7%), palmitic acid (1%), stearic acid (1%), oleic acid (3%), linoleic acid (4.2%), linolenic acid (0.3%) and eicosanoic acid (0.3%). Castor oil is available in a variety of grades from several suppliers.
The most preferred plasticizers are those that contain sufficient ether, hydroxyl, and/or polyol linkages to enhance the breathability of the formulation.
A variety of liquid surfactants may be employed in the breathable composition of the present invention as a plasticizing diluent. Suitable surfactants include nonionic, anionic, and silicone surfactants. Exemplary nonionic surfactants are:
Ethoxylates of (i) C sub 1-C sub 18, preferred C sub 8-C sub 9 alkyl or dialkyl phenols, such as those sold under the tradenames Macol DNP-10, available from PPG Industries, Gurnee, Ill., a 10 mole ethoxylate of dinonyl phenol, and Triton X-100, available from Union Carbide, a 10 mole ethoxylate of octyl phenol; (ii) alkyl C sub 8-C sub 60 mono-alcohols, such as those sold under the tradenames Surfonic L-12-8, an 8 mole ethoxylate of dodecanol, available from Huntsman Chemical Co., and Unithox 480, a 38 mole ethoxylate crystalline surfactant available from Petrolite Specialty Polymers Group, Tulsa, Okla.; and (iii) propylene oxide polymers, such as those sold under the tradename Pluronic, which are ethylene oxide/propylene oxide block copolymers having Mn of 200 to 3000 available from BASF; and benzoates formed by partial ondensation of benzoic acid with hydrophilic di or mono-ols having less than 1000 Mn, such as the product of condensing about three equivalents of benzoic acid with four equivalent of diethylene glycol, commercially available as XP 1010 from Velsicol Chemical. A preferred nonionic surfactant blend is Atmer 685, available from ICI Surfactants (Wilmington, Del.).
Suitable anionic surfactants are: C sub 8-C sub 60 alkyl ethoxylate sulfonates, (CH sub 3 xe2x80x94(CH sub 2) sub 11-14 xe2x80x94(Oxe2x80x94CH sub 2 CH sub 2) sub 3 xe2x80x94SO sub 3-Na sup +, such as, Avenel S30, available from PPG Industries; alkyl C sub 8-C sub 60 sulfonates, such as, Rhodapon UB (C sub 12 xe2x80x94SO sub 3 sup-Na sup+) available from Rhone Poulenc; sorbitan ester available as Atmer 100 from ICI Surfactants; and alkyl/aromatic sulfonates, such as those sold under the tradename Calsoft.
Suitable silicone surfactants are ethoxylates or propoxylates of polydimethyl siloxane, having a number average molecular weight of 500 to 10,000, preferably 600 to 6000, such as are sold under the tradenames Silwet L-77, L-7605, and L-7500 available from OSi Specialties, Danbury, Conn.; and product 193 from Dow Corning.
The preferred surfactants exhibit a relatively low molecular weight that tends to improve the compatibility in the adhesive formulations. The maximum acceptable molecular weight depends on the type of surfactant and the solubility and/or compatibility with the polymer employed in the formulation.
The breathable thermoplastic composition of the present invention may comprise one or more tackifying resins particularly if the composition is intended to adhere one or more substrates (in addition to forming a barrier layer). The tackifying resins useful herein are generally polar in nature and have a Ring and Ball softening point greater than 60xc2x0 C. and include any compatible resins or mixtures thereof such as natural and modified rosins such as gum rosin, wood rosin, tall oil rosin, distilled rosin, hydrogenated rosin, dimerized rosin, and polymerized rosin; rosin esters such as glycerol and pentaerythritol esters of natural and modified rosins such as, for example, the glycerol ester of pale, wood rosin, and the glycerol ester of hydrogenated rosin, the glycerol ester of polymerized rosin, and the pentaerythritol ester of hydrogenated rosin, and the phenolic-modified pentaerythritol ester of rosin; phenolic modified terpene or alpha methyl styrene resins as well as the hydrogenated derivatives thereof such as the resin product resulting from the condensation in an acidic medium of a bicyclic terpene and a phenol.
Representative examples of preferred tackifiers include Foral NC, Kristalex 3100 (100xc2x0 C. melt point) and 3085 (85xc2x0 C. melt point) and Endex, hydrogenated alpha methyl styrene resins available from Hercules (Wilmington, Del.); non-ionic materials such as Foral AX also from Hercules, alpha methyl styrene phenolics such as Uratak 68520 from DSM Resins (Panama City, Fla.), rosin esters such as Unitac R100L available from Union Camp, terpene phenolic tackifiers such as Nirez 300, V2040 and 2019 available from Arizona Chemical (Panama City, Fla.).
The breathable thermoplastic composition of the present invention may further comprise a wax in an amount up to about 30 wt-%, more preferably at an amount ranging from about 3 wt-% to about 20 wt-%, and most preferably from about 5 wt-% to about 15 wt-%. Waxes are particularly useful for decreasing the surface tack of the barrier film layer. Waxes useful herein are preferably polar in nature. Polar waxes are those which contain at least one polar functional group such as hydroxyl, amide, sulfone, phosphate, sulfonamide, urethane, carboxylate acid, amine, and carbonate. The concentration of the functional group is present in an amount greater than about 2xc3x9710xe2x88x923 equivalents per gram and preferably greater than 3.5xc3x9710xe2x88x923 equivalents per gram. The molecular weight of waxes ranges from about 200 g/mole to about 1000 g/mole. Representative examples including 12-hydroxystearamide, N-(2-hydroxy ethyl 12-hydroxystearamide and N,Nxe2x80x2ethylene bis 12-hydroxystearamide (PARICIN 220 and PARICIN 285 respectively, from CasChem, Bayonne, N.J.), stearamide (Kemamide S from Witco, Memphis, Tenn.), glycerin monostearate, sorbitan monostearate, and 12-hydroxy stearic acid. Also useful alone or in combination with the above are less polar waxes such as N,Nxe2x80x2-ethylene-bis stearamide (Kemamide W-40 from Witco), linear aliphatic long chain alcohols (Unilin 425 from Petrolite, Tulsa, Okla.), hydrogenated castor oil (castor wax), oxidized synthetic waxes, and functionalized waxes such as oxidized homopolymers and oxidized polyethylene waxes (Petrolite E-1040). The Applicants have found that polar waxes having a melt point greater than 70xc2x0 C., preferably greater than about 110xc2x0 C., and more preferably about 140xc2x0 C. or greater, are particularly advantageous.
A variety of other polymers, tackifiers and additives such as antioxidants (Irganox 1010), pigments and fillers, particularly hydrophilic fillers such as starch or cellulose esters and acetates, may be employed in an amount up to about 10 wt-% provided such materials do not detract from the humidity resistance, blocking resistance and speed of moistenability contributed by the blend of crystalline water sensitive polymer with amorphous water sensitive polymer.
Radiation curable compositions for use in the invention are those compositions that can be applied as a continuous layer, attain their desired film properties by virtue of being crosslinked upon exposure to a radiant energy source such as electron beam (EB) or ultraviolet (UV). Similarly, as in the case of compositions which are not radiation responsive, the breathability is contributed by having a sufficient amount of oxygen linkages dispersed throughout the film layer such that after curing the film/film layer has a WVTR of at least 100 g/m2/day.
Whether or not the resulting film layer is breathable, curable compositions typically possess low initial viscosities and can develop high film strengths by the crosslinking during curing. For such embodiments exhibiting sufficient film strength, the layer may be self-supporting. Hence, the composition need not be coated onto a reinforcement material. Hence, in the case of the preferred coating method as described in U.S. Pat. No. 5,827,252, the substrate being coated may be a release coated roller rather than a material such as a nonwoven that becomes part of the finished article.
Radiation curable compositions that find utility for breathable films/barrier layer applications include acrylated polyesters commercially available from H.B. Fuller Company under the tradename SolarCure as well as acrylated branched polyesters available as Dynacoll A from Creanova. The branched structure results in amorphous character. The hydroxyl containing polyesters are subsequently reacted with acrylic functional adducts as described in U.S. Pat. No. 4,822,829 yielding an acrylated polyester which are responsive to both UV and EB radiation. In the case of UV curing, a photoinitiator is also required.
Depending on the molecular weight (Mn), which is typically below 15,000 atomic mass units (amu""s), the compounded or neat acrylated polyesters can be applied at temperatures ranging from 60xc2x0 C. to 120xc2x0 C. Exposure to a radiant energy source results in an immediate cure that increases the molecular weight and intramolecular crosslinking.
The acrylated polyesters have been found to exhibit high WVTR even after crosslinking. Several of the Solarcure grades of acrylated polyester are pressure sensitive in a neat, unformulated state allowing them to be amenable to creating fluid impermeable barrier film layers that simultaneously serve an adhesive function. In the case of feminine napkins, bandages, etc., this would eliminate the need to have a separate barrier layer coated with an adhesive. The pressure sensitivity or film properties can be enhanced by the addition of other polymers, tackifying resins, and plasticizers. Alternatively, for applications in which pressure sensitivity is undesirable, other grades of acrylated polyesters may be employed or the surface tack may be diminished with compounding.
Additional radiation curable ingredients that exhibit utility for radiation curable breathable films/film layers include the Kraton KLP (Kraton Liquid Polymers available from Shell) and acrylic polymers such as Acrynol DS 3429 and DS 3458, available from BASF. The Kraton KLP contains reactive epoxy linkages and is compounded with hydroxyl terminated polymers and photoinitiator to yield a photoreactive composition, whereas the Acrynol contains bound photoinitiator in some degree of reactive unsaturation. These polymers can also be formulated into compositions that are useful for creating breathable films/film layers upon irradiation to provide the desired properties.